This invention relates generally to wind turbines, and more particularly to methods and apparatus for reducing peak loads of wind turbines such as those that occur in a changing wind environment.
Recently, wind turbines have received increased attention as environmentally safe and relatively inexpensive alternative energy sources. With this growing interest, considerable efforts have been made to develop wind turbines that are reliable and efficient.
Generally, a wind turbine includes a rotor having multiple blades. The rotor is mounted to a housing or nacelle, which is positioned on top of a truss or tubular tower. Utility grade wind turbines (i.e., wind turbines designed to provide electrical power to a utility grid) can have large rotors (e.g., 30 or more meters in diameter). Blades on these rotors transform wind energy into a rotational torque or force that drives one or more generators, rotationally coupled to the rotor through a gearbox. The gearbox steps up the inherently low rotational speed of the turbine rotor for the generator to efficiently convert mechanical energy to electrical energy, which is fed into a utility grid.
Wind turbines are designed to shut down under high yaw error conditions. However, known wind turbines utilize a single “allowable” yaw error set point to initiate high yaw error shutdowns to limit loads. For example, a yaw error trigger may trigger a shutdown procedure when the rotor is angled at more than 45 degrees from the direction of the wind for more than three seconds. This single allowable yaw error may not be an optimum condition to initiate a shutdown for all wind speed conditions. Thus, the wind turbine may experience higher than desired loads under some conditions.